Turbocharger having a turbocharger housing comprising a threaded connection by means of an anchor

ABSTRACT

A turbocharger has a turbocharger housing with a bearing housing and at least one impeller housing. The bearing housing and the impeller housing are screwed together by way of a screw anchor connection, and at least one head of an anchor of the screw anchor connection is covered by a cover element.

The invention relates to a turbocharger with a turbocharger housing, consisting for example of a turbine housing, a compressor housing and a bearing housing, which has a threaded connection by means of tie-rods.

A turbocharger normally consists of an exhaust gas turbine in an exhaust gas flow, connected by way of a turboshaft to a compressor in the intake system. To this end a turbine wheel and a compressor wheel for example are supported in a rotatable manner on the turboshaft. The turbine wheel here is accommodated in a turbine housing of the turbocharger and the compressor wheel is accommodated in a corresponding compressor housing. Both housings are connected to one another by way of a bearing housing. The turbine wheel of the turbine is made to rotate by the exhaust gas flow of the engine and thereby drives the compressor wheel of the compressor. This causes the compressor to increase the pressure in the intake system of the engine so that a larger quantity of air enters the cylinder during the intake stroke. This means that more oxygen is available and a correspondingly larger quantity of fuel can be combusted. This allows the power output to be increased, as the mean pressure of the engine and its torque increase.

Exhaust gas turbochargers, wherein a turbine housing has a threaded connection by way of tie-rods, are known from the patent application by Siemens with the reference number 10 2007 017 824.9. The turbine housing is screwed to the bearing housing by way of a number of tie-rods here for example.

This threaded tie-rod connection has the advantage that it ensures an extremely reliable threaded connection. It is however disadvantageous if the screw heads and their cylindrical counterbores are located in the region of the compressor diffuser and therefore in the region of high flow speeds. This can result in efficiency losses due to turbulence.

It is also known from the prior art, as disclosed for example in DE 698 27 307 T2, that the turbine housing can be connected by way of so-called short screws instead of a threaded tie-rod connection. Here the turbine housing is screwed firmly to a flange on an opposite side of the bearing housing with the compressor housing being screwed correspondingly to a flange at the other end of the bearing housing.

However this has the disadvantage that production and assembly are considerably more complex, as corresponding holes have to be provided on the bearing housing and the compressor and turbine housings. Also a plurality of screws has to be screwed. It is also not possible to achieve the same threaded connection reliability as with the threaded tie-rod connection.

The object of the present invention is therefore to provide a turbocharger with a turbocharger housing, wherein the housing can be screwed using a threaded tie-rod connection but wherein the occurrence of turbulence due to the threaded tie-rod connection can at least be reduced.

This object is achieved by a turbocharger with a turbocharger housing with the features of claim 1.

Thus according to the invention a turbocharger with a turbocharger housing is provided:

-   -   wherein the turbocharger housing has a bearing housing and at         least one impeller housing and     -   wherein the bearing housing and the impeller housing are screwed         together by means of a threaded tie-rod connection, and     -   wherein at least one head of a tie-rod of the threaded tie-rod         connection is covered with a cover element.

The turbocharger here has the advantage that on the one hand the turbocharger housing can be provided with a threaded tie-rod connection that ensures a highly reliable threaded connection. On the other hand the heads of the tie-rods are covered so that turbulence can be at least significantly reduced or even essentially prevented, so that the efficiency of the impeller housing is not impaired.

Advantageous embodiments and developments of the invention will emerge from the subclaims and the description with reference to the drawings.

In one inventive embodiment the impeller housing is a turbine housing and/or a compressor housing. This means that according to the invention both the turbine housing and the compressor housing can essentially be secured with one threaded tie-rod connection.

In a further inventive embodiment the cover element covers one, a number of or all the heads of the tie-rods of the threaded tie-rod connection at least partially or completely. This has the advantage that when air or exhaust gas flow past the tie-rod screws, turbulence can at least be substantially reduced, as air does not flow directly past the heads of the tie-rod screws and the corresponding counterbores in the housing but is shielded from these by the cover element.

In another inventive embodiment the cover element is configured as at least partially or completely closed. The cover element can also optionally be provided with through openings, which are precisely large enough for a tool to engage with an assigned tie-rod. This likewise provides only the smallest possible contact surface for turbulence.

According to a further embodiment of the invention the cover element is positioned in a holder on the impeller housing and/or the bearing housing. The holder here can be a recess or projection, to which the cover element is secured. Alternatively or additionally the cover element can also be secured by means of a threaded connection or similar. The threaded connection here is provided in a region where if possible there is no or very little turbulence.

In a further embodiment of the invention the cover element is configured as part of a wall of a diffuser of the impeller housing. This has the advantage that this does not essentially impair the efficiency of the impeller housing and the cover element can have the double function of covering the heads of the tie-rods and providing a wall of the impeller housing. This can save assembly and production costs.

In another inventive embodiment the cover element is for example a cover sheet. Such cover sheets have the advantage that they are easy to produce and are easy to shape, to be configured for example as a wall of a diffuser of an impeller housing, as described above.

According to a further embodiment of the invention the cover element is for example a stopper element to cover at least one head of a tie-rod. The stopper element here can have the form of a cap, which encloses the screw head. Such a cap is easy to produce and is easily fitted. In one alternative embodiment the stopper element can also have a plate with a projection or plug, which can be inserted into a head of a tie-rod. The plate here can be level with the screw head or can project at least partially or completely beyond it, for example to cover the screw head and a counterbore in the bearing housing at least partially or completely. Such a stopper element is also easy to produce and fit. The stopper element can also be configured so that the plate has not only one but a number of projections or plugs to cover a number of tie-rod heads at the same time.

The invention is described in more detail below with reference to the exemplary embodiments shown in the figures in the drawings, in which:

FIG. 1 shows a schematic section of a turbocharger with a turbocharger housing, wherein the housing has a direct threaded connection according to the prior art;

FIG. 2 shows a schematic section of a turbocharger with a turbocharger housing, wherein the housing is provided with a threaded tie-rod connection according to one embodiment of the invention; and

FIG. 3 shows a section of the turbocharger with the turbocharger housing according to FIG. 2, also showing the compressor housing and the bearing housing, and

FIGS. 4 a, 4 b show examples of a stopper element as the cover element.

Identical or functionally identical elements and apparatuses are shown with the same reference characters in all the figures, unless otherwise specified.

FIG. 1 shows a schematic section of a turbocharger housing 10 according to the prior art, which is part of a turbocharger (not shown). The turbocharger housing 10 and/or its turbine housing 28 is screwed directly to a bearing housing 14 here with relatively short screws 12. To this end the bearing housing 14 has a flange 16 at its end opposite the turbocharger housing 10, to which flange 16 the turbocharger housing 10 is screwed firmly by means of a number of screws 12, as shown in FIG. 1. The screw heads 18 of the screws 12 here are outside the bearing housing 14 and turbine housing 10, so that no turbulence can result, which would lead to reduced efficiency. However this construction has the disadvantage that it is complex to assemble and does not provide a reliable threaded connection, unlike the threaded tie-rod connection. This also becomes clear in the comparison of the threaded tie-rod connection and direct threaded connection below.

Below is a comparison of a threaded tie-rod connection and a direct threaded connection. An M6 tie-rod is used as the tie-rod here and a hexagon head screw M6×15 is used as the screw for the direct threaded connection.

Tie-rod M6 Mean temp. tie-rod 300° C. Mean temp. bearing housing (BH) 280° C. Rp0.2 at 300° C. 540 N/mm² Utilization 1 Elongation 50 mm E modulus 210000 N/mm² Thermal expansion coefficient tie-rod 17.4 1/K Thermal expansion coefficient BH 13 1/K Pretensioning force 10854 N Length change due to force fit 0.12857143 mm Length change due to temp. 0.261 mm Length change BH due to temp. 0.182 mm Residual elongation 0.04957143 mm Residual pretensioning 4184.82 N

Hexagon head screw M6x15 (direct threaded connection) Mean temp. tie-rod 500° C. Mean temp. bearing housing (BH) 320° C. Rp0.2 at 300° C. 540 N/mm² Utilization 1 Elongation 5 mm E modulus 210000 N/mm² Thermal expansion coefficient tie-rod 17.4 1/K Thermal expansion coefficient BH 13 1/K Pretensioning force 10854 N Length change due to force fit 0.01285714 mm Length change due to temp. 0.0435 mm Length change BH due to temp. 0.0208 mm Residual elongation −0.00984286 mm Residual pretensioning −8309.34 N

It can be seen from the determination of the individual parameters that the threaded tie-rod connection (screw head bearing on compressor-side flange of bearing housing, long screw) only shows a small loss of pretensioning compared with the direct threaded connection with short screws. The improvement is achieved by way of the overall much greater elongation and the lower mean temperature of the tie-rod. The direct threaded connection (screw head bearing on turbine-side flange of bearing housing, short screw) also requires a higher-quality screw material because of the higher component temperature.

FIG. 2 shows a schematic section of a turbocharger 20 with a turbocharger housing 10, according to one embodiment of the invention. The turbocharger 20 here has a turboshaft 22, on one side of which a turbine wheel 24 is supported and on the other side of which a compressor wheel 26 is supported. The turboshaft 22 is disposed in a bearing housing 14 here. The turbine wheel 24 is disposed in a turbine housing 28 here and the compressor wheel 26 is disposed correspondingly in a compressor housing, the compressor housing not being shown in FIG. 2 for reasons of clarity.

In contrast to the prior art, because the turbine housing 28 and compressor housing respectively are screwed directly to the bearing housing 14, a threaded tie-rod connection 30 is provided according to the invention. The turbine housing 28 is screwed to the bearing housing 14 here at its end opposite the compressor housing (screw head bearing on compressor-side flange of bearing housing) by way of at least one or more tie-rod screws 32. The tie-rod 32 here for example requires a counterbore 34 in the bearing housing 14, in which its screw head 36 is sunk. It is scarcely possible here to avoid positioning the tie-rod head 36 in the region for example of a compressor diffuser of the compressor housing (not shown here). Since air flows past at high speed here, the head 36 and its counterbore 34 can cause turbulence. This turbulence can result in a deterioration in compressor efficiency.

According to the invention therefore the head 36 of the tie-rod 32 is covered for the air flowing past so that turbulence can be at least significantly reduced or essentially prevented. A cover element 38 here can be a cover sheet 40 for example, which is disposed in front of the head 36 of the tie-rod 32 and covers it at least partially or preferably essentially completely. A corresponding holder 42 in the form of a recess 44 for example can be provided for this purpose in the turbocharger housing 10, the cover element 40 being inserted therein. The cover element 38 can be configured as closed or can have small or just sufficiently large through openings for a tool to engage with the tie-rod 32.

The cover element 38 can for example also be configured at the same time as part of a wall 46 of a diffuser 48 of a compressor housing 50, as described below with reference to FIG. 3. At least one cover element 38 can be provided here, to cover all the heads 36 of the tie-rods 32 or a number of cover elements 38, depending on structural conditions. The cover element 38 can be symmetrical, for example rotationally symmetrical, depending on the structural conditions of the bearing housing 10 or the core assembly and the adjoining turbine or compressor housing 28, 50. However it does not have to be symmetrical but can have any form.

Optionally or additionally the head 36 of the tie-rod 32 can also be covered with a stopper element 52 as the cover element 38. Two examples of such stopper elements 52 are illustrated in the following FIGS. 4 a and 4 b.

FIG. 3 also shows a section of the turbocharger 20 with the turbocharger housing 10 according to FIG. 2, the compressor housing 50 and bearing housing 14 also being illustrated here. The turbine housing 28 here is screwed by way of one tie-rod 32 or a number of tie-rods 32 to a side of the bearing housing 14 opposite the compressor housing 50 (screw head bearing on compressor-side flange 54 of bearing housing 14).

To cover the head 36 of the tie-rod 32 a corresponding cover element 38 is provided, which is held for example in a holder 42 of the turbocharger housing 10 or the core assembly. The cover element 38 can however optionally also be additionally secured, for example by means of threaded connections or similar. This applies to all embodiments of the invention.

The cover element 38 here is for example a cover sheet 40, which is shaped as described above so that it forms a part of a wall 46 of the diffuser 48 of the compressor housing 50. It is thus possible to prevent or significantly reduce turbulence, which would otherwise result without the cover element 38. In the present instance the turbulence can be reduced to such a degree that it does not have a negative effect on efficiency.

FIGS. 4 a and 4 b show two examples of stopper elements 52 as cover elements 38, it being obvious to the person skilled in the art that there is a plurality of possible variations here. The first stopper element 38 in FIG. 4 a is configured for example in the manner of a cap 56, which encloses the screw head 36. The cap 56 can be configured so that it projects to the side beyond the head 36 of the tie-rod 32, as shown with a broken line, in order also to cover for example the counterbore 34 in the bearing housing 14 at least partially or completely. It is also possible here to configure a type of strip on which a number of such caps are configured, in order thus to cover a row of heads 36 of tie-rod screws 32, it being possible to cover the counterbore 34 in the bearing housing 14 at least partially or completely at the same time.

The second stopper element 52 in FIG. 4 b is configured with a plate 58 with a projection 60 or plug, which is inserted into the recess 62 in the respective screw head 36. The plate 58 of the stopper element 52 can project beyond the screw head, in order for example to cover the screw head 36 and the counterbore 34 in the bearing housing 14 at least partially or completely. It is also possible here for the plate 58 of the stopper element 38 to be configured in the form of a strip with a number of projections 60 and to extend over a number of screw heads 36. Alternatively the second stopper element 38 can be configured with a cap 56 instead of the projection 60 or in addition to it, as shown with a broken line in FIG. 4 b.

Stopper elements 38 can also be provided, which are inserted into the gaps 64 formed by the counterbore 34 laterally or peripherally at the heads 36 to cover such gaps 64. The heads 36 can themselves be covered with a stopper element according to FIG. 4 a or 4 b, it being possible for the plate 58 of the stopper element 38 in FIG. 4 b to be level with the head 36 of the screw 32 to be covered.

The cover elements 38 described above can be made for example of metal or metal sheet. It is also possible in principle in particular on the compressor side for the cover elements 38 to be made for example of a suitable rubber or hard rubber, as the compressor side does not get as hot as the turbine side.

Although the present invention has been described above with reference to preferred exemplary embodiments, it is not restricted to these but can be modified in many ways. The embodiments described above can be combined with one another for this purpose, in particular individual features thereof.

In particular all the embodiments described above can be applied both to the compressor housing 50 and to the turbine housing 28. This means that not only can the turbine housing 28 be secured to the bearing housing 10 by way of a threaded tie-rod connection 30, with at least one corresponding cover element 38 being provided to cover the heads 36 of the tie-rods 32, but the threaded tie-rod connection 30 and provision of the cover element 38 can also be applied correspondingly to the compressor housing 50. The compressor housing 50 can thus be screwed likewise to the bearing housing 10 by way of a threaded tie-rod connection 30, like the turbine housing 28 in FIGS. 2 and 3. 

1-12. (canceled)
 13. A turbocharger, comprising: a turbocharger housing formed with a bearing housing and at least one impeller housing; a tie-rod connection between said bearing housing and said impeller housing screwing said bearing housing and said impeller housing to one another; said tie-rod connection including a threaded tie-rod having at least one head; and a cover element disposed to cover said at least one head of said threaded tie-rod of said tie-rod connection and for reducing, or preventing, turbulence of air and/or exhaust gas flowing past.
 14. The turbocharger according to claim 13, wherein said impeller housing is at least one of a turbine housing and a compressor housing.
 15. The turbocharger according to claim 13, wherein said cover element covers one head of said tie-rod at least partially or completely.
 16. The turbocharger according to claim 13, wherein said tie-rod is one of a plurality of tie-rods each having a head, and said cover element is configured to cover a plurality or all of said heads of said plurality of tie-rods at least partially or completely.
 17. The turbocharger according to claim 13, wherein said cover element is at least partially closed.
 18. The turbocharger according to claim 13, wherein said cover element is completely closed.
 19. The turbocharger according to claim 13, wherein said cover element is formed with at least one opening configured to enable a tool to engage the respective said tie-rod.
 20. The turbocharger according to claim 13, which comprises a holder disposed on said impeller housing and/or said bearing housing, and wherein said cover element is positioned in said holder.
 21. The turbocharger according to claim 13, wherein said cover element forms a part of a wall of a diffuser of said impeller housing.
 22. The turbocharger according to claim 13, wherein said cover element is a cover sheet.
 23. The turbocharger according to claim 13, wherein said cover element is a stopper element for covering a head of a tie-rod.
 24. The turbocharger according to claim 23, wherein said stopper element has the form of a cap enclosing said head of said tie-rod.
 25. The turbocharger according to claim 23, wherein said head of said tie-rod is a screw head.
 26. The turbocharger according to claim 23, wherein said stopper element has a plate formed with a projection for insertion into said head of said tie-rod, enabling said plate to be level with said head or to project beyond said head.
 27. The turbocharger according to claim 26, wherein said stopper element is formed to cover said head and a counter-bore formed in said bearing housing at least partially or completely.
 28. The turbocharger according to claim 13, wherein said cover element is formed of, or contains, at least one material selected from the group consisting of a metal, a metal alloy, plastic, and rubber.
 29. The turbocharger according to claim 13, wherein said cover element is made of hard rubber or contains hard rubber. 